The present invention relates to a metallic insert pipe which is designed to be placed inside a metallic die set as an insert member when producing an insert molded article by injection molding, a method for processing such an insert pipe, and a molded article having an insert pipe buried therein, and can be applied to various technical fields including those involving power transmission shaft members such as pipe shafts, lead screws and shafts integrally carrying cams and gears, and optical fiber connector ferrules.
The inventor of this application previously proposed a lead screw, a pipe shaft and a method and metallic die set for molding such articles in Japanese patent publication (kokoku) No. 5-52765, as a power transmission shaft member having a metallic insert pipe buried therein as an insert member.
The power transmission shaft member such as a lead screw and a pipe shaft according to this proposal is produced in the following manner. A metallic pipe having a large number of through holes passed through the outer circumferential wall thereof is placed in a metallic die set adapted to the outer contour of the power transmission shaft member, and resin material is injected into the metallic pipe in the axial direction. The resin material initially fills the interior of the metallic pipe, and then flows to the exterior of the metallic pipe via the through holes. As a result, a power transmission shaft member having a prescribed outer contour is produced with the metallic pipe and the resin material molded into a single body.
The metallic pipe serving as the insert member is typically made of hard metallic material such as stainless steel, and is provided with a large number of holes passed through the outer circumferential wall thereof. When these holes are formed by a laser beam, the material surrounding the hole may be deformed by generation of strains and deposition of sputters, and such strains and sputters are required to be removed by grinding and other methods. The thinning and annealing of the material surrounding the hole which occur as a result of grinding and laser radiation, respectively, tend to make the material surrounding the hole brittle, and reduce the mechanical strength thereof.
When an insert molding is carried out by burying a metallic pipe in the molded article, sink marks tend to develop near the axial end portions inside the metallic pipe, and around the holes. In particular, when there is any deformation around the holes due to strains and sputter deposition, the mold quality of the insert molded article such as a lead screw which requires a high level of dimensional precision tends to be impaired. When the mechanical strength of the part surrounding the holes is reduced, the bonding between the metallic pipe and the resin material is impaired. Such a reduction in the bonding strength could lead to serious consequences in the case of molded articles such as optical fiber connector ferrules which require a high level of axial dimensional precision.
A conventional optical fiber connector ferrule typically consists of an inner portion including a large bore for receiving a sheathed core of an optical fiber cable, and a small bore for receiving an exposed (glass) core of the optical fiber cable, and an outer portion comprising a radially projecting flange portion, and is generally formed as a metal ferrule, as disclosed, for instance, as prior art in FIG. 8 of Japanese patent publication (kokoku) No. 5-36762, titled as xe2x80x9coptical connector and method for producing an optical connector ferrulexe2x80x9d.
Such a ferrule requires a grinding finish to ensure the necessary level of positioning precision, and not suited for mass production with an added disadvantage of a high production cost. The above cited patent publication includes a proposal to provide a novel method for producing a ferrule which addresses such problems.
According to the proposed method for producing a ferrule, the metallic pipe is placed in the metallic die set, and a sheathed optical fiber core having a part of the sheath removed and thereby exposing part of the optical fiber core is received in the metallic pipe. Two ferrules are simultaneously molded, and then cut apart into two ferrules.
According to this production method, because a pair of ferrules are jointly molded, and are then cut into two parts, the coaxial precision of the ferrules can be improved, but a highly complex post-processing is required to achieve a favorable optical connecting surface. The post-processing includes the steps of cutting the jointly molded assembly at a part of the metallic pipe, and finishing the cut end surfaces of the metallic pipe and the core wire of the optical fiber cable.
In view of such problems of the prior art, a primary object of the present invention is to provide an insert pipe for injection molding which can be more integrally bonded to the resin material than has hitherto been possible.
A second object of the present invention is to provide an insert pipe for injection molding which has a number of through holes passed through the outer circumferential wall thereof and is from the problems which would be produced if the through holes are formed by a laser beam.
A third object of the present invention is to provide an insert pipe for injection molding which can prevent sink marks from being developed in the outer surface of the molded article.
A fourth object of the present invention is to provide a method which can fabricate such an insert pipe both economically and easily.
A fifth object of the present invention is to provide a molded article having a pipe insert molded therein which may consist of a power transmission shaft member such as a pipe shaft, a lead screw and a shaft rod integrally carrying a cam or gear, and an optical fiber ferrule.
According to the present invention, such objects can be accomplished by providing an insert pipe for injection molding, wherein: a plurality of through holes are passed through an outer circumferential wall of a metallic pipe, and each of said through holes comprises an opening, and at least one raised piece formed by bending, typically inwardly, a wall part of said metallic pipe adjacent to said opening.
According to the insert pipe of the present invention, the raised piece raised from the edge of the opening reinforces the edge of the opening, and prevents the deformation of the metallic pipe when subjected to stress either during the process of injection molding or during use. When the insert pipe is buried in the molded article, the raised piece is also effective as an engagement member for increasing the bonding force between the insert pipe and the resin material and preventing the development of sink marks resulting from the volumetric shrinking of the resin material. Typically, said opening is polygonal in shape, and said raised piece is raised from each side of said polygonal opening. For application of the present invention to a molded article, the through holes are typically arranged along both circumferential and axial directions in said metallic pipe. In case of a lead screw, the through holes are typically arranged in a spiral pattern so as to correspond the threaded section of the molded article.
When a molded article is produced by using such an insert pipe, the molded article additionally includes an inner molded portion molded inside said insert pipe; and an outer molded portion molded outside said insert pipe and connected to said inner molded portion via said openings. Thus, the insert pipe is firmly embedded in the molded article because the inner molded portion and the outer molded portion are integrally connected with each other via the through holes, and the overall mechanical strength can be increased. In particular, the raised piece contributes to the increase in the bonding force between the molded part and the insert pipe as well as increasing the mechanical strength of the insert pipe itself. Also, the enhanced bonding force contributes to the prevention of sink marks which typically arise from the volumetric shrinking of the resin material. By virtue of such properties, the molded article of the present invention is particularly advantageous for use as a power transmission shaft, a lead screw, and an optical fiber ferrule.
The present invention additionally provides a method for processing an insert pipe for injection molding, comprising the steps of: placing a metallic pipe in a shape retaining support assembly in an open state, said assembly comprising a plurality of shape retaining support members each having an arcuate shape retaining surface so as to jointly define a cavity for closely surrounding an outer profile of said metallic pipe; moving said shape retaining support members so as to closely surround said metallic pipe with said shape retaining surfaces of said shape retaining support members; and passing piercing punches through holes defined in said shape retaining support assembly so as to form through holes in said metallic pipe in a prescribed pattern, said piercing punches being adapted in such a manner that each of said holes comprises an opening, and at least one raised piece formed by bending a wall part of said metallic pipe adjacent to said opening. To form such a raised piece in a simple and reliable manner, each of the piercing punches may be provided with a pyramidal point. The pyramidal point may have any desired number of sides depending on the number of raised pieces that are desired to be formed on each through hole. Even a conical point may used. In this case, the raised piece may have the shape of an irregular burr or the shape of a crown.
Thus, by using a corresponding number of piercing punches, a large number of through holes can be formed simultaneously without causing any localized stress or deformation to the insert pipe while ensuring a high level of dimensional precision because the shape retaining support assembly prevents the insert pipe from deformation and can keep the cross section of the pipe member in true circle. By placing the piercing punches in an appropriate pattern, it is possible to form through holes arranged in a spiral pattern or in any desired pattern. Also, the apparatus for implementing this method can be constructed at a relatively low cost, and is suitable for mass producing such insert pipes.
Because the part surrounding each communication hole is not strained or deformed by the deposition of sputters, as opposed to the forming of such holes with a laser beam, grinding and other post-processing is not required. Also, the part surrounding each communication hole is not made brittle due to grinding or annealing resulting from radiation of a laser beam, and the mechanical strength of the insert pipe is therefore ensured.
In particular, when the present invention is applied to an insert pipe molded article which has a distinctive feature on the exterior thereof such as a lead screw or other power transmission shaft member, it is effective in ensuring the coaxial precision of the outer contour thereof. When it is applied to an insert pipe molded article which has a distinctive feature in the interior thereof such as an optical connector ferrule, it is effective in ensuring the coaxial precision of the inner contour thereof. In this manner, the present invention can be effectively applied to a wide range of insert pipe molded articles.